This invention relates generally to processes for treating radioactive liquid wastes in installations such as, for example, nuclear power stations.
One known method of treating a radioactive liquid waste produced from a nuclear power station comprises heating and vaporizing the radioactive liquid waste with heating steam so as to thereby concentrate the waste and reduce its volume.
More specifically, the features of this known method, and apparatus therefor are as follows. A radioactive liquid waste discharged from an installation such as, for example, a nuclear power station is stored in a liquid supply tank, from which it is transferred by a liquid supply pump to an evaporation concentration device. This evaporation concentration device normally comprises a concentration vessel which is generally of the vertical type. A steam heater is installed in the concentration vessel or, alternatively, in a circulation circuit path including the concentration vessel and a circulation pump. This steam heater operates to heat the above mentioned radioactive liquid waste thus supplied to the evaporation concentration device, whereby the liquid waste is evaporated and concentrated to a specific concentration.
The vapor generated by the above described heating process is conducted to a condenser where the same is cooled and rendered into a condensate. On the other hand, the waste solution concentrated as described above is discharged into a storage tank for concentrated waste solution after the operation of the above mentioned evaporation concentration device and liquid supply pump has been terminated.
In the above described process, however, there is the possibility of the heating tube of the steam heater becoming corroded and being damaged or broken depending on the properties of the radioactive liquid waste being treated. If this damage should occur, since the pressure of the heating steam is higher than the internal pressure of the evaporation concentration device when this device is operating, there is little possibility of the heating steam line being contaminated. However, when the operation of the evaporation concentration device is terminated, the heating steam condenses within the steam heater and is replaced by the concentrated waste solution within the evaporation concentration device, whereby, when the operation of the evaporation concentration device is restarted, this concentrated waste solution is introduced into the heating steam line and gives rise to operational difficulties such as, for example, radioactive contamination of the entire heating steam line.